Angular testing async pipe does not trigger the observable

I want to test a component that uses the async pipe. This is my code:

@Component({
selector: 'test',
template: `
<div>{{ number | async }}</div>
`
})
class AsyncComponent {
number = Observable.interval(1000).take(3)
}

fdescribe('Async Compnent', () => {
let component : AsyncComponent;
let fixture : ComponentFixture<AsyncComponent>;

beforeEach(
async(() => {
TestBed.configureTestingModule({
declarations: [ AsyncComponent ]
}).compileComponents();
})
);

beforeEach(() => {
fixture = TestBed.createComponent(AsyncComponent);
component = fixture.componentInstance;
fixture.detectChanges();
});


it('should emit values', fakeAsync(() => {

tick(1000);
fixture.detectChanges();
expect(fixture.debugElement.query(By.css('div')).nativeElement.innerHTML).toBe('0');

});


But the test failed. It's seems Angular does not execute to Observable from some reason. What I am missing?

When I'm trying to log the observable with the do operator, I don't see any output in the browser console.

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